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Atomic Annie
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Mockup W48 155mm artillery shell
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Shortly after the creation of the first atomic bombs, the US became interested in weapons with 'limited' yield that could be used tactically, rather than strategically. One of the more interesting of these developments was atomic artillery, first tested in Nevada on May 25th 1953.
Some major design hurdles needed to be overcome to develop an artillery-fired atomic projectile (AFAP). Nuclear weapons of the time were large, highly complex and delicate devices, intrinsically unsuited for firing out of a cannon. An artillery shell is usually spun at up to 15,000 revolutions per minute for stability, and subjected to crushing accelerations up to 18,000 times the force of gravity. This meant the device needed to have an absolute minimum of moving parts, and those that were included needed to be extremely shock resistant.
The design was approved by the Pentagon, largely due to the intervention of Samuel Feltman, the chief of the ballistics section of the ordnance department's research and development division. After a three-years of development, Robert Schwartz (the engineer who created the preliminary designs) released the first AFAP designated 'TX-9' from the Army's Picatinny Arsenal in Dover.
In its simplest form, the shell was a 'gun-type' weapon, except with sufficient ruggedness to withstand the stress of being launched from a gun barrel. Utilizing highly enriched uranium in one large ring assembly, and one smaller 'bullet' fired down a tube into the ring assembly to achieve critical mass. The forces of setback, the movement of internal components toward the rear of shell when fired, and spin, were used to arm the device when the shell was fired.
The W-9 finally contained more than 60 kilograms of oralloy; its predicted yield was only 15 KT, but its nuclear efficiency was less than two percent. By comparison, the nuclear efficiency of contemporary implosion bombs was between 25% and 35%. This inherent inefficiency meant that this weapon was extremely expensive in relation to its yield.
The scientists at Los Alamos had originally wanted to tower test the Mk-9 shell. A static test would enable more precise measurements of the device in operation. Collection of this data from a spinning, encased device traveling at several hundred meters per second was considerably more difficult. Although standard measurements could be done, the shell would need to be detonated at no more than 150 meters above ground.
However, the Joint Chiefs of Staff (JCS) concluded that substantial benefits would accrued from a full-scale nuclear test of the MK 9/280MM gun delivery system, before its deployment to "vital areas", namely Korea.
Deployment
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M-65 280mm field artillery piece
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The largest field artillery piece available at the time was the 240mm howitzer, too small to accommodate the new weapon. This requirement led to the development of the M-65 280mm Nuclear Field Artillery piece, nicknamed 'Atomic Annie'. The name was probably chosen with reference to 'Anzio Annie', a massive German Krupp K5 railroad gun that had battered the Anzio beachhead during 1944. These enormous 283mm artillery pieces were capable of firing a 255kg projectile up to 64km.
The gun traveled suspended between the front and rear custom transporter tractors, each with its own 365 hp engine, independently driven much like an aerial ladder fire truck. The speed of the transporter on the open road was about 30 mph, but its weight of 76 tons precluded it from crossing unreinforced bridges or driving on soft roads. The gun was initially designated T131 and the carriage was T72.
Once deployed, the gun sat on a turntable pedestal and three jacks. The tremendous firing forces were absorbed by a double recoil system. Both the gun tube and the heavy carriage moved separately with the recoil, reducing the overall recoil distance to a minimum. This system removed the requirement for any prior excavation work reducing setup time.
The Test
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Crew taking cover before firing
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Two 280 mm cannons were taken by rail from Oklahoma, to the Nevada test site 100 km north of Las Vegas. The cannons were then emplaced side-by-side on a flat area 11 km south of Frenchman flats by an artillery battalion who had been specifically trained for the task at Fort Bliss in Texas.
The assembly and preparation for firing took only an hour, including time for insertion of nuclear components into the shells, and the manual setting of the height of burst fuse. In spite of this, the gun would later be criticized for being too vulnerable to air attack or artillery counter-battery fire. This was compounded by the requirement for several adjustment and registration (spotting) rounds to be fired prior to the main shot, to zero-in the gun.
The crew then took position in trenches or behind barricades, before firing the cannon remotely at 08:30 hours local time. The shot was designated Grable (mnemonic code for gun), the tenth atmospheric test shot of Operation Upshot-Knothole.
The shell travelled 10,000 meters before detonating 26 meters west, 41 meters south and 7 meters above what had been the intended burst point above Frenchman Flat in the NTS. It achieved a nominal yield of 15 kilotons, the same explosive force as the three meter long, four ton Little Boy bomb dropped over Hiroshima nearly eight years earlier.
The test codenamed 'Grable' was attended by the Chairman-delegate of the Joint Chiefs of Staff, Admiral Arthur W. Radford and United States Secretary of Defense Charles Erwin Wilson. This was the first and only nuclear shell to be fired from a cannon.
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Shot "Grable" - Yield 15Kt
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As the initial flash subsided, a unique phenomenon was observed. The fireball had split into two separate halves, in effect a 'double fireball'. This unexplained phenomenon was not seen again until four years later with shots Priscilla and Owens during Operation Plumbbob.
The second anomaly was the formation of a precursor, a second shock front ahead of the incident wave. Formed as the shock wave reflected off the ground and surpassed the incident wave and Mach stem. It resulted in a lower overpressure, but higher overall dynamic pressure, inflicting far greater damage on drag sensitive targets. Far greater in fact than the previous shot Encore, which had been nearly twice the yield.
The low burst height (necessitated by the difficulties of gathering test data from an artillery shell), and the dust laden layer of heated air close to the ground (known as 'popcorning'), were also significant contributors to this anomalous increase in destructive blast effects. This led to a complete recalculation of existing blast-curve data, and strategists to rethink the importance of low air bursts in tactical nuclear warfare. These phenomena were investigated in full later during shot MET of Operation Teapot.
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Precurser wave video
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700 DOD personnel, including the Secretary of Defence and several congressmen witnessed the shot from an area about 11 km north of ground zero. The test was also experienced by 2,600 troops stationed in trenches 4.5 km west of ground zero, as participants of exercise Desert Rock V. These troops then attacked two targets 2.5 km from ground zero, but were forced back by high winds and dust.
The test of the 280MM cannon no doubt impressed the North Korean and Chinese governments, who were in the process of concluding an armistice with United Nations forces in Korea during the Upshot-Knothole series in the spring of 1953. (During the 16th century, the "upshot" was the final shot in an archery tournament.)
After the test Sterling Cole, the Chairman of the congressional Joint Committee on Atomic Energy, stated:
"In order to understand the military importance of our progress, one has only to recall that the 1945 bomb was so big as to require four-engine B-29 bomber to carry it to Hiroshima and Nagasaki in World War II. The projectile fired in today's test was just over 11 inches in diameter. They have concentrated into capsule form what once filled an entire bomb bay.. We have added another major weapon to our stockpile""
After the successful test, at least 20 cannons were manufactured at Watervliet and Watertown Arsenals, at a cost of US$800,000 each. The cannons weighed 83 tons, were 25m long, 5m wide, and 3.7m tall. Operated by a crew of 5 to 7 artillerymen, the cannon fired 280mm caliber shells that weighed 272kg with a range of 32km. The yield of the shells could be anywhere from 15-20 kilotons.
They were deployed to Europe and Korea, and frequently shifted around to avoid being detected and targeted by opposing forces. Due to the size of the apparatus, their limited range, the development of nuclear shells compatible with existing artillery pieces, and the development of rocket and missile based nuclear artillery effectively made the M65 obsolete soon after it was deployed.
However, it remained a prestige weapon and was not retired until 1963.
Four 280mm cannons still exist in various locations throughout the US. Atomic Annie is located at Fort Sill, the other three are at the National Atomic Museum in Albuquerque, New Mexico; Fort Riley, Kansas and Aberdeen Proving Ground in Maryland.
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